The long range goal of this research is to contribute to an understanding of how the regulation of nuclear gene activity occurs in a typical eucaryotic cell. Our particular concern is with how a gene on one chromosome regulates the expression of genes on other chromosomes. The regulatory system chosen for study is the galactose/melibiose utilization pathway in yeast. The system consists of five structural genes specifying five inducible enzymes and two genetically well defined regulatory genes, a positive regulatory gene and a negative regulatory gene, which control enzyme inducibility at the level of transcription. Two major, interrelated lines of research are being developed. The first is aimed at understanding how the interplay between positive and negative regulatory gene expression controls the induction of structural enzyme gene expression. The strategy here is to first identify and purify the positive and negative regulatory gene products; then study their modes of action. The second major line of research is aimed at determining the existence, distribution, and nature of positive regulatory recognition sites adjacent to four cloned enzyme structural genes. Our approach will be to use standard DNA sequencing methodology and the purified positive regulatory gene product to seek out recognition sites common to the coordinately regulated cloned genes. We anticipate that the proposed lines of research will generate a variety of significant and useful information regarding the mechanisms of positive and negative regulation in this eucaryotic system.